1. Field of the Invention
The present invention relates to a process for the preparation of amorphous polymers of propylene.
The invention also relates to a process for the preparation of indene compounds suitable as metallocene ligands.
2. Description of the Prior Art
As it is well known, products of propylene homopolymerization can be either crystalline or amorphous. Whereas the polypropylene having isotactic or syndiotactic structure is crystalline, the polypropylene having essentially atactic structure appears to be amorphous. The atactic polypropylene, in the representation by the Fischer formula as described in xe2x80x9cM. Farina, Topics Stereochem., 17, (1987), 1-111xe2x80x9d shows methyl groups casually arranged from one or the other side of the polymeric chain. As described in the above mentioned publication, useful information on the structure can be obtained from N.M.R. analysis.
The amorphous polypropylene available on the market is mainly used in adhesive compositions and as additives for bitumens. Generally, it is a by-product of the isotactic polypropylene obtained in the presence of catalysts of the Ziegler-Natta type. The separation of small fractions of amorphous polypropylene from the remainder product however involves inconvenient separation processes with solvents.
More recently, in the polymerization reaction of olefins, catalysts based on metallocene compounds and alumoxane compounds have been used. Operating in the presence of these catalysts, polymers characterized by a narrow molecular weight distribution and endowed with structural characteristics of interest can be obtained.
In particular, by polymerizing propylene in the presence of metallocene catalysts, depending on the metallocene used crystalline or amorphous polypropylene can be obtained. However, the amorphous polypropylene obtainable in the presence of metallocene catalysts is generally endowed with low molecular weight.
U.S. Pat. No. 4,542,199 describes a catalytic system for the polymerization of olefins comprising a bis(cyclopentadienyl)zirconium and an alumoxane. From the polymerization reaction of propylene carried out in the presence of this catalyst, low molecular weight atactic polypropylene is obtained.
European patent application 283,739 describes a catalytic system for the polymerization of olefins comprising a partially substituted bis(cyclopentadienyl)zirconium and an alumoxane. From the polymerization reaction of propylene carried out in the presence of this catalyst, low molecular weight atactic polypropylene is obtained.
In U.S. Pat. No. 4,931,417, catalysts for the polymerization of olefins comprising a metallocene compound wherein two cyclopentadienyl rings are joined through a radical containing a silicon or germanium atom are described. The polymerization reaction of propylene carried out in the presence of these compounds partially substituted on the cyclopentadienyl rings gives rise to isotactic polypropylene, whereas with dimethylsilandiylbis(cyclopentadienyl)zirconium dichloride, low molecular weight atactic polypropylene is obtained.
In European patent application 399,347 a process for the polymerization of propylene in the presence of a catalyst comprising a metallocene having a cyclopentadienyl ring and a fluorenyl ring joined by a bridge, such as isopropylidene-(9-fluorenyl)(3-methylcyclopentadienyl)zirconium dichloride is described. An amorphous polypropylene is obtained, the structure of which however is not atactic, but is defined as syndioisoblocks. Namely, it is a structure wherein syndiotactic and atactic sequences alternate.
The international application WO 94/11406 describes a class of indenyl compounds substituted in the 2-position on the indenyl group. In the application it is stated that these compounds can be used as catalyst components for the polymerization of olefins. However, in the polymerization examples only homopolymers of ethylene and elastomeric copolymers of ethylene with propylene are prepared.
It has now been found that it is possible to prepare substantially amorphous polymers of propylene having high molecular weight, operating at temperatures of industrial interest, by carrying out the polymerization reaction of propylene in the presence of metallocene catalysts comprising particular bis-indenyl or bis-4,5,6,7-tetrahydroindenyl compounds substituted in the 2-position on the indenyl or tetrahydroindenyl groups.
Therefore, an object of the present invention consists of a process for the preparation of substantially amorphous polymers of propylene, comprising the polymerization reaction of propylene in the presence of a catalyst comprising the product of the reaction between:
(A) a metallocene compound selected from the bis-indenyl compounds of formula (I): 
xe2x80x83and the corresponding bis-4,5,6,7-tetrahydroindenyl compounds, wherein:
on each indenyl or tetrahydroindenyl group the substituents R1 and R2, same or different from each other, are hydrogen atoms, xe2x80x94CHR2 groups or xe2x80x94CHRxe2x80x94 groups form a cycle comprising from 3 to 8 carbon atoms, wherein the R substituents are hydrogen atoms, C1-C20 alkyl radicals, C3-C20 cycloalkyl radicals, C2-C20 alkenyl radicals, C6-C20 aryl radicals, C7-C20 alkaryl radicals or C7-C20 aralkyl radicals and can contain Si or Ge atoms;
the substituents R3, R4, R5 and R6, same or different from each other, are defined as R substituents, in addition two adjacent R3, R4, R5 and R6 substituents on the same ring can form a ring comprising from 5 to 8 carbon atoms; M is a transition metal atom of groups IVb, Vb or VIb of the Periodic Table;
substituents X, same or different from each other, are hydrogen atoms, halogen atoms, xe2x80x94R7, xe2x80x94OR7, xe2x80x94SR7, xe2x80x94NR72 or xe2x80x94PR72 groups where substituent R7 are defined as substituent R; optionally pre-reacted with an organometallic compound of aluminium of formula AlR83 or Al2R86, wherein substituents R8, same or different, are defined as substituent R or are halogen atoms; and
(B) at least a compound selected from (a) the organo-metallic compounds of aluminum containing at least a heteroatom selected from oxygen nitrogen and sulphur, optionally in admixture with an organometallic compound of aluminum of formula AlR83 or Al2R86, wherein substituents R8, same or different, are defined as above, and (b) compounds capable of producing a metallocene alkyl cation.
Another object of the present invention is a process for the preparation of indene compounds of formula (VII): 
suitable as metallocene ligands, which comprises the reaction of an aromatic compound of formula (VIII) with a compound of formula (IX), to obtain the indan-1-one of formula (X), wherein R3, R4, R5 and R6 have the above defined meaning, R10 is a hydrogen atom or an alkyl radical C1-C3, Y is an halogen atom, according to the following reaction scheme: 
and the following conversion into the corresponding indene (VII).
Among the metallocene compounds of formula (I), the preferred are those wherein, in each of the indenyl or tetrahydroindenyl groups the substituents R3 are the same as substituents R6, and substituents R4 are the same as substituents R5. More preferred are those in which all the substituents R3 and R6 are hydrogen atoms.
The transition metal M is preferably selected from titanium, zirconium, hafnium and vanadium, more preferably zirconium.
The substituents X are preferably chlorine atoms or a methyl radical.
Non limiting examples of metallocene compounds which can be used in the process of the present invention are:
bis(2-methyl-indenyl)zirconium dichloride,
bis(2,4,7-trimethyl-indenyl)zirconium dichloride,
bis(2,4,6-trimethyl-indenyl)zirconium dichloride,
bis(2,5,6-trimethyl-indenyl)zirconium dichloride,
bis(2,4,5,6,7-pentamethyl-indenyl)zirconium dichloride,
bis(2-ethyl-indenyl)zirconium dichloride,
bis(2-ethyl-4,7-dimethyl-indenyl)zirconium dichloride,
bis(2-ethyl-4,6-dimethyl-indenyl)zirconium dichloride,
bis(2-ethyl-5,6-dimethyl-indenyl)zirconium dichloride,
bis(2-ethyl-4,5,6,7-tetramethyl-indenyl)zirconium dichloride,
bis(2-propyl-indenyl)zirconium dichloride,
bis(2-propyl-4,7-dimethyl-indenyl)zirconium dichloride,
bis(2-propyl-4,6-dimethyl-indenyl)zirconium dichloride,
bis(2-propyl-5,6-dimethyl-indenyl)zirconium dichloride,
bis(2-propyl-4,5,6,7-tetramethyl-indenyl) zirconium dichloride,
bis(2-methyl-indenyl)zirconium dimethyl,
bis(2,4,7-trimethyl-indenyl)zirconium dimethyl,
bis(2,4,6-trimethyl-indenyl)zirconium dimethyl,
bis(2,5,6-trimethyl-indenyl)zirconium dimethyl,
bis(2,4,5,6,7-pentamethyl-indenyl)zirconium dimethyl,
and the corresponding bis-4,5,6,7-tetrahydroindenyl compounds.
Alumoxanes usable in the catalyst of the invention are, for example, linear, cyclic or branched alumoxanes containing at least one group of the type (II): 
where the substituents R9, same or different from each other, are R1 or a group xe2x80x94Oxe2x80x94Al(R9)2, and optionally some R9 may be halogen atoms.
In particular, alumoxanes of formula (III) may be used: 
in the case of linear compounds where n is 0 or an integer of from 1 to 40 and the substituents R9 are defined as substituents R1, or alumoxanes of formula (IV): 
in the case of cyclic compounds, with n which is an integer of from 2 to 40, and the substituents R9 are defined as the substituents R1.
Substituents R9 are preferably methyl, ethyl, isobutyl.
Examples of alumoxanes suitable to be used according to the present invention are methylalumoxane (MAO) and isobutyl-alumoxane (TIBAO).
The alumoxanes used in the process of the present invention may be obtained by reaction between water and a organometallic compound of aluminum of formula AlR83 or Al2R86, in which the substituents R8, same or different from each other, are defined as above, with the condition that at least one R8 is different from halogen. In that case these are made to react in a molar ratio of Al/water of from about 1:1 to 100:1.
Non limiting examples of the aluminum compound of formula AlR83 or Al2R86 are:
Al(Me)3, Al(Et)3, AlH(Et)2, Al(iBu)3, AlH(iBu)2, Al(iHe)3, Al(C6H5)3, Al(CH2C6H5)3, Al(CH2CMe3)3, Al(CH2SiMe3)3, Al(Me)2iBu, Al(Me)2Et, AlMe(Et)2, AlMe(iBu)2, Al(Me)2iBu, Al(Me)2Cl, Al(Et)2Cl, AlEtCl2, Al2(Et)3Cl3, where Me=methyl, Et=ethyl, iBu=isobutyl, iHe=hexyl. Trimethyl aluminum (TMA) and triisobutyl aluminum (TIBAL) are preferred.
A particular class of organo-metallic compounds of aluminium minium used in the catalyst according to the invention are those obtainable by the reaction of water with the aluminum alkyl or alkylhydride in which at least one alkyl is not linear, in a molar ratio Al/H2O of from 1:1 to 100:1. Compounds of this type are described in the European patent application No. EP-575.875, the content of which is herein intended as incorporated in the present description.
Organo-metallic compounds of aluminum useable in the catalyst according to the invention are, in addition, those of formula (V): 
or of formula (VI): 
where R1 is defined as above.
The molar ratio between the aluminum and the metal of the metallocene compound is in general from about 10:1 to about 10000:1, and preferably from about 100:1 to about 5000:1.
Non limiting examples of the compound capable of forming alkyl metallocene cations are compounds of formula Y+Zxe2x88x92, where Y+ is a Brxc3x6nsted acid, capable of donating a proton and of irreversibly reacting with substituent X1 or X2 of the compound of formula (I) and Zxe2x88x92 is a compatible anion, which does not coordinate, which is capable of stabilizing the active catalytic species which originates from the reaction of the two compounds, and is sufficiently labile in order to be removed by an olefinic substrate. Preferably the anion Zxe2x88x92 comprises one or more boron atoms. More preferably the anion Zxe2x88x92 is an anion of formula Bar4(xe2x88x92), where the substituents Ar, same or different from each other, are aryl radicals such as phenyl, pentafluorophenyl, bis(trifluoromethyl)phenyl. Particularly preferred is the tetrakis-pentafluorophenyl-borate. In addition, compounds of formula BAr3 may be conveniently used. compounds of this type are described, for example, in the published International patent application WO 92/00333, the content of which is incorporated in the present description.
The catalysts of the present invention may also be used on inert supports. That is what is obtained by depositing the metallocene compound (A), or the product of reaction of the latter with component (B), or component (B) and subsequently the metallocene compound (A), on an inert support such as, for example silica, alumina, styrene-divinylbenzene copolymer, polyethylene or polypropylene.
A particularly suitable class of inert supports used in the process of the present invention are porous organic supports functionalized with functional groups having active hydrogen atoms. Particularly preferred are those in which the organic support is a partially crosslinked styrene polymer. These supports are described in the European patent application EP-633,272, the content of which is incorporated in the present description.
The solid so obtained, in combination with further additions of the alkyl aluminum compound, either as such or pre-reacted with water, if necessary, is usefully used in gas phase polymerisation.
The metallocene compounds of formula (I) can be prepared by reaction of the corresponding. indenyl or tetrahydroindenyl ligands with a compound able to form a delocalized anion on the cyclopentadienyl ring, and then with a compound of formula MX4, wherein M and the substituents X are defined as above.
In the case in which at least a substituent X of the metallocene compound of formula (I) to be prepared is different from a halogen, it is necessary to substitute at least a substituent X in the obtained metallocene with at least a substituent X different from halogen.
The reaction of substitution of substituents X with substituents X different from halogen is carried out with commonly known methods. For instance, when the desired substituents X are alkyl groups, the metallocenes can be allowed to react with alkylmagnesium halides (Grignard reactives) or with lithium alkyl compounds.
In the particularly advantageous process for the preparation of indene compounds of formula (VII): 
according to the present invention, the indan-1-ones (X) can be converted in the corresponding indenes (VII) by different methods.
For instance, the indan-1-ones (X) can first be converted to the indan-1-oles and than dehydrated.
Reducing agents suitable for use in the reduction reaction are, for instance, lithium aluminum hydride and sodium boron hydride.
The dehydration reaction can be performed in the presence of an acid such as, for instance, p-toluen-sulphonic acid.
The propylene polymers obtainable with the process of the present invention are endowed with an atactic structure and, therefore, they are substantially amorphous. Their melting enthalpy (xcex94Hf) is generally not measurable.
The molecular weight of the above-described propylene polymers can even be very high. In fact the intrinsic viscosity can reach very high values, up to 10 dl/g and above.
The molecular weights of the propylene polymers, in addition to being high, are distributed over relatively limited ranges. An index of molecular weight distribution is represented by the ratio Mw/Mn which is preferably less than 4, more preferably less than 3.
13C-N.M.R. analysis gives information on the tacticity of the polymeric chain, that is the distribution of the relative configuration of the tertiary carbons.
The structure of the propylene polymer appears substantially atactic. Nevertheless, it is observed that the isotactic diads (m) appear to be more numerous than the syndiotactic diads (r). Namely, %(m)xe2x88x92%(r) greater than 0, preferably %(m)xe2x88x92%(r) greater than 5 and, more preferably %(m)xe2x88x92%(r) greater than 10.
The Bernoullianity index (B), defined as:
xe2x80x83B=4 [mm][rr]/[mr]2
has values near unity, generally in the range 0.7-1.3, preferably in the range 0.8-1.2.
In the process of the invention, the polymerization reaction of propylene can be carried out in the presence of one or more olefins selected from ethylene and the xcex1-olefins containing from 4 to 20 carbon atoms. Non limitative examples of these xcex1-olefins are 1-butene, 1-pentene, 1-hexene, 1-octene and 1,5-hexadiene.
In particular, with the process of the present invention it is possible to prepare substantially amorphous copolymers of propylene with small quantities, that is up to about 10% by mole, of comonomeric units.
The possibility of obtaining directly, as the only product of the polymerization reaction of propylene, a substantially amorphous polypropylene endowed with high molecular weight is an advantage over the traditional processes.
The process of the polymerization of olefins according to the invention may be carried out in liquid phase, optionally in the presence of an inert hydrocarbon solvent, or in gas phase. The hydrocarbon solvent. may be aromatic such as toluene, or aliphatic, such as propane, hexane, heptane, isobutane, and cyclohexane.
The polymerization temperature is generally from xe2x88x92100xc2x0 C. to +80xc2x0 C., and more preferably from xe2x88x9250xc2x0 C. to +50xc2x0 C. The lower the polymerization temperature, the higher the molecular weight of the polymer obtained results.
In particular, by the process of the invention propylene polymers may be obtained having molecular weights of industrial interest at relatively high temperatures. The molecular weight of the polymers obtained in the presence of the catalysts of the invention are in any case higher with respect to those polymers obtained with the corresponding catalysts in which the indenyl group of the metallocene compound is not substituted in the 2-position.
The molecular weight of the polymer may be in addition varied, by varying the type or concentration of the catalytic components or by using molecular weight regulators such as, for example, hydrogen.
The molecular weight distribution may be varied by using mixtures of different metallocenes, or by carrying out the polymerization in more steps which differ in the polymerization temperature and/or the concentration of the molecular weight regulator.
The polymerization yield depends on the purity of the metallocene component of the catalyst. Moreover the metallocene compound obtained by the process of the invention may be used as such or may undergo purification treatment.
The different catalyst components may be put into contact before the polymerization. The contact time is generally from 1 to 60 minutes, preferably from 5 to 20 minutes. The concentration of the pre-contact for the metallocene component (A) are from 10xe2x88x922 to 10xe2x88x928 mol/l, while for component (B) are from 10 to 10xe2x88x923 mol/l. The precontact is generally carried out in the presence of a hydrocarbon solvent and, optionally, small quantities of monomer.